Method and apparatus for sensing seat occupant weight

ABSTRACT

A system for measuring the weight of a seat occupant is used to control airbag deployment. The system is incorporated into a vehicle seat supported on inboard and outboard track assemblies. The inboard and outboard track assemblies are mounted to a vehicle structure such that a center track portion remains unsupported. A first sensor assembly is mounted to the inboard track assembly and a second sensor assembly is mounted to the outboard track assembly. The first sensor assembly generates a first signal in response to measuring deflection of the inboard track assembly due to seat occupant weight. The second sensor assembly generates a second signal in response to measuring deflection of the outboard track assembly due to seat occupant weight. A central processor determines seat occupant weight based on the first and second signals. The central processor communicates with the airbag system to control the deployment of the airbag based on seat occupant weight.

RELATED APPLICATION

This application claims priority to provisional application 60/120,637filed on Feb. 24, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for measuring theweight of a seat occupant. Specifically, a sensor arrangement is mountedwithin a vehicle seat track to provide accurate seat occupant weightmeasurements.

2. Related Art

Most vehicles include airbags and seatbelt restraint systems that worktogether to protect the driver and passengers from experiencing seriousinjuries due to a high speed collision. It is important to control thedeployment force of the airbags and the force of the seatbeltpretensioners based on the size of the driver or the passenger. One wayto control these forces is to monitor the weight of the seat occupant.If a smaller person such as a child or infant in a car seat is in thepassenger seat, the weight on the seat will be less than if an adultoccupies the seat.

Current systems for measuring the weight of a seat occupant are complexand expensive. One type of system uses pressure sensitive foil matsmounted within the seat bottom foam. Another system uses sensors placedat a plurality of locations within the seat bottom. The combined outputfrom the mats or the sensors is used to determine the weight of the seatoccupant. These sensors experience a substantially vertical force, dueto the weight of the seat occupant, but are also subject to longitudinaland lateral forces caused by acceleration, deceleration, or turning. Thelateral and longitudinal forces picked up by the sensor incorporate anerror component into the weight measurement. The sensors are verysophisticated using multiple strain gages and complicated bendingelements to provide high measurement sensitivity in the verticaldirection and low sensitivity to lateral and longitudinal forces inorder to increase accuracy.

Mounting these sensors within the seat bottom can also be difficult andtime consuming. It is difficult to find mounting locations for each thesensors that will accommodate all of the various positions of a seatedoccupant while still providing accurate measurements. Further, shiftingof the occupant on the seat can dislodge or move the sensors out oftheir proper location. Because the sensors are mounted within the seatbottom, it is difficult to reposition the sensors after the seat isinstalled in the vehicle.

Thus, it is desirable to have a simplified seat occupant weightmeasurement system that is accurate and easily to install and overcomesthe above references deficiencies with prior art systems.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a system for measuring theweight of an occupant seated on a vehicle seat includes a track assemblythat is used to support a vehicle seat. The track assembly includes afirst track mounted to a vehicle structure and a second track supportedfor movement relative to the first track. The tracks are deflectable ina vertical direction due to an occupant weight force exerted on theseat. At least one sensor is mounted on the tracks for generating asignal representative of the occupant weight force.

In a preferred embodiment, the track assembly is comprised of an inboardtrack assembly and an outboard track assembly spaced apart from theinboard track assembly. A first sensor assembly is mounted to theinboard track assembly for generating a first signal in response tomeasuring deflection of the inboard track assembly due to seat occupantweight. A second sensor assembly is mounted to the outboard trackassembly for generating a second signal in response to measuringdeflection of the outboard track assembly due to seat occupant weight.The system uses a central processor to determine seat occupant weightbased on the first and second signals. The system also preferablyincludes an airbag control module that is in communication with theprocessor. Deployment force of an airbag is controlled by the controlmodule based on seat occupant weight.

A method for determining the weight of a seat occupant includes thefollowing steps. An inboard seat track assembly is mounted to a vehiclestructure and an outboard seat track assembly is spaced apart from theinboard seat track assembly and mounted to the vehicle structure. Theinboard and outboard seat track assemblies are defined by apredetermined cross-sectional area and each track assembly has at leastone track segment with a cross-sectional area that is less than thepredetermined cross-sectional area. The method steps includes mounting afirst sensor assembly in the track segment of the inboard seat trackassembly, mounting a second sensor assembly in the track segment of theoutboard seat track assembly, generating a first signal from the firstsensor assembly in response to deflection of the inboard track assemblydue to seat occupant weight, generating a second signal from the secondsensor assembly in response to deflection of the outboard track assemblydue to seat occupant weight, and combining the first and second signalsto determine seat occupant weight.

Additional steps include providing a system controller for controllingdeployment of an airbag and generating a seat occupant weight signalbased on the combination of the first and second signal. The seatoccupant weight signal is transmitted to the controller and thedeployment force of the airbag is controlled based on the seat occupantweight.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a vehicle with an airbag system andan occupant sitting in a seat with the airbag in an active state shownin dashed lines.

FIG. 2 is a side view of a seat assembly incorporating the subjectweight measurement system.

FIG. 3 is a side view of the seat track assembly of FIG. 2.

FIG. 3A is a magnified view of the section 3A indicated in FIG. 3.

FIG. 4 is a cross sectional view of the track assembly taken along lines4-4 of FIG. 3.

FIG. 5 is a schematic view of a control system for the subject weightmeasurement system.

FIG. 6 is a schematic view of the sensors mounted within the subjecttrack assembly.

FIG. 7 is a schematic view representing a full bending bridge.

FIG. 8 is a schematic view of the sensors mounted within the subjecttrack assembly having an overload mechanism.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

A vehicle includes a vehicle seat assembly, shown generally at 12 inFIG. 1, and an airbag system 14. The seat assembly 12 can be either adriver or passenger seat and includes a seat back 16 and a seat bottom18. When a vehicle occupant 20 is seated on the seat 12 a vertical forceFv is exerted against the seat bottom 18. The vertical force Fvrepresents the weight of the seat occupant 20.

The airbag system 14 deploys an airbag 24 under certain collisionconditions. The deployment force for the airbag 24, shown in dashedlines in FIG. 1, varies according to the weight of the occupant 20. Thevehicle includes a unique system for measuring the weight of the seatoccupant 20. This unique system is installed within a seat trackassembly, generally indicated at 26 in FIG. 2.

The seat track assembly 26 includes a first track member 28 mounted to avehicle structure 30 such as a floor, frame, or riser, for example. Asecond track member 32 is supported for movement relative to the firsttrack member 28 along a longitudinal axis 34. First 38 and secondsensors 40 are mounted on one of the track members 28, 32. The sensors38 and 40 are used to generate a signal representative of the occupantweight. The first sensor 38 is preferably positioned rearwardly and thesecond sensor 40 positioned forwardly on the track assembly 26. Thefirst 38 and second 40 sensors are used to measure deflection of thetrack assembly 26 to generate the signal.

The first track member 28 includes a forward end 42 and a rearward end44 with a central track portion 46 extending between the ends 42, 44.The forward 42 and rearward 44 ends are mounted to the vehicle structure30 such that the central track portion 46 remains unsupported to formgap 48 between the vehicle structure 30 and the central track portion46. Preferably, the first track member 28 is mounted to a riser 50having upwardly extending supports 52 at each end for attachment to theforward 42 and rearward 44 ends of the first track member 28.

Thus, the central track portion 46 of the seat track assembly 26 isdeflectable under load. When the occupant is seated on the seat 12, avertical force Fv is exerted against the track assembly 26, as shown inFIG. 3. Reaction forces Fr are exerted in the opposite direction. Theforces cause the central track portion 46 to deflect and reflect fullbending beam behavior, shown generally at 54 in FIG. 3A. The sensors arepreferably strain gages 38, 40 that are positioned along the centraltrack portion 46, however, other types of sensors known in the art couldalso be used. For example, fiber optic or magneto elastic sensors couldbe used.

The sensors 38, 40 are preferably positioned in the first track member28 such that the sensors 38, 40 remain positioned in the unsupportedtrack section as the second track member 32 adjusts horizontally alongaxis 34. As shown in FIG. 4, a plurality of ball bearings 56 areinstalled between the track members 28, 32 such that the second trackmember 32 can slide easily relative to the first track member 28. Thebearings 56 also transfer the forces applied to the second track member32 to the rigid track portion 46 between the two (2) sensor locations.

As shown in FIG. 5, the seat 12 is mounted to the vehicle structure 30on an inboard track assembly 26 a and an outboard track assembly 26 bthat is spaced apart from the inboard track assembly 26 a by apredetermined distance. The inboard 26 a and outboard 26 b trackassemblies are mounted to have similar bending behavior, i.e. both trackassemblies 26 a, 26 b are deflectable in a vertical direction due to anoccupant weight force. Both the inboard 26 a and outboard 26 b trackassemblies include first 28 and second 32 track members.

In one embodiment, first 28 and second 32 sensors are installed in theinboard track assembly 26 a and third 58 and fourth 60 sensors areinstalled in the outboard track assembly 26 b. The first 38 and second40 sensors generate a first signal 62 representative of the portion ofoccupant weight on the inboard track assembly 26 a and the third 58 andfourth 60 sensors generate a second signal 64 representative of theportion of occupant weight on the outboard track assembly 26 b. Thesignals 62, 64 are transmitted to an electronic control unit (ECU) 66,which combines the signals to determine the weight of the occupant 20.The ECU then sends a control signal 68 to a system controller 70.Preferably, the system controller 70 is an airbag control module that isin communication with the ECU 66 such that the deployment force of theairbag 24 is controlled based on seat occupant weight. The systemcontroller 70 could also be used to control the force of seat beltpretensioners based on occupant weight.

While the above configuration is preferred, an option configurationcould utilize one sensor assembly mounted to the inboard track assemblyfor generating the first signal 62 in response to measuring deflectionof the inboard track assembly 26 a due to seat occupant weight and asecond sensor assembly mounted to the outboard track assembly 26 b forgenerating the second 64 signal in response to measuring deflection ofthe outboard track assembly 26 b due to seat occupant weight.

As shown in greater detail in FIGS. 6, the track assembly 26 has apredetermined cross-sectional area defined by height H1. A portion,generally indicated at 72, of each track assembly 26 has across-sectional area defined by H2 that is less than the predeterminedcross-sectional area H1. Each track assembly 26 a, 26 b has two (2)track portions 72 with this decreased cross-sectional area. One sensorassembly 38, 40, 58, 60 is mounted in each track portion 72. Only thefirst sensor assembly 38 is shown in FIG. 6. As the track assembly 26deflects under load, the sensor assembly 38 measures full bending beambehavior 54, shown in FIG. 7. Each of the sensors 38, 40, 58, 60 at thefour (4) locations thus serves as a Wheatstone Bridge for measuringdeflection. The operation of a Wheatstone Bridge is well known in theart.

Preferably, the reduced cross-sectional area track portions 72 arecreated by forming square shaped holes within the first track member 28.The holes create dual-beam spring elements. With such elements locatedon the inboard 26 a and outboard 26 b track assemblies, it is possibleto measure the vertical force Fv applied on the area between the twosets of tracks 26 a, 26 b.

The method for determining the weight of a seat occupant includes thefollowing steps. An inboard seat track assembly 26 a is mounted to avehicle structure 30 and an outboard seat track assembly 26 b is spacedapart from the inboard seat track assembly 26 a and mounted to thevehicle structure 30. The inboard 26 a and outboard 26 b seat trackassemblies are defined by a predetermined cross-sectional area H1 andeach track assembly 26 a, 26 b has at least one track segment 72 with across-sectional area H2 that is less than the predeterminedcross-sectional area H1. The method steps include mounting a firstsensor assembly in the track segment 72 of the inboard seat trackassembly 26 a and mounting a second sensor assembly in the track segment72 of the outboard seat track assembly 26 b. A first signal 62 isgenerated from the first sensor assembly in response to deflection ofthe inboard track assembly 26 a due to seat occupant weight. A secondsignal 64 is generated from the second sensor assembly in response todeflection of the outboard track assembly 26 b due to seat occupantweight. The first 62 and second 64 signals are used to determine seatoccupant weight.

Additional steps include providing a system controller 70 forcontrolling deployment of an airbag 24 and generating a seat occupantweight signal 68 based on the combination of the first 62 and second 64signals. The seat occupant weight signal is transmitted to thecontroller and the deployment force of the airbag is controlled based onthe seat occupant weight.

Other steps include providing the inboard 26 a and outboard 26 b trackassemblies with forward ends 42 and rearward 44 ends interconnected by acenter portion 46 and fixing the forward 42 and rearward 44 ends to avehicle structure 30 such that the center portion 46 of each trackassembly 26 a, 26 b remains unsupported. The track segment 72 ispreferably located in the center portion 46.

As discussed above, the first sensor assembly is preferably comprised offirst 38 and second 40 sensors that are mounted in the first trackmember 28 of the inboard track assembly 26 a. The second sensor assemblyis preferably comprised of third 58 and fourth 60 sensors that aremounted in the first track member 28 of the outboard track assembly 26b.

A seat track assembly 26 with integrated weight sensors 38, 40, 58, 60is provided to determine the weight of an occupant 20 seated on avehicle seat 12. It is preferable to integrate the sensors 38, 40, 58,60 into the seat track assembly 26 because it is a common component formost vehicle seats 12. The subject weight measurement system is easilyincorporated into any type of seat track configuration. The weightsensors 38, 40, 58, 60 are mounted within reduced size track segments 72to measure deflection of the track material caused by the weight of theoccupant 72. The measured weight is independent of seat positions and isaccurately provided in various occupant positions on the seat 12.

By measuring the deflection in all four (4) locations in the inboard 26a and outboard 26 b track assemblies, it is possible to calculate theoccupant weight, which is proportional to the sum of the output of allof the sensors 38, 40, 58, 60. The center of gravity of the upper partof the seat and the occupant can be calculated by subtracting the sum ofthe sensor signals in the front from the sum of the sensor signals inthe rear and dividing the result by the sum of all four (4) signals. Theelectronics for signal conditioning can be housed within the trackassemblies 26 a, 26 b as is well known in the art.

Under high overload conditions, the track assembly 26 experiences highvertical Fv and horizontal Fh forces. These forces cause the track toexperience an overload resultant force Fre that will try to separate thetrack 26 from the floor 30. In applications, with heavy overloadconditions, like seats having integrated or all-belts-to seatconfigurations, it is beneficial to integrate an active overloadprotection. One such method of protection utilizes an overload bolt 74,shown in FIG. 8, extending through the track members 28, 30 to thevehicle floor 30. Under high vehicle impact forces, the bolt 74 preventsthe track assembly 26 from separating from the floor 30. Thus, thereduced cross-sectional areas 72 do not have to sustain the full impactforces.

Although a preferred embodiment of this invention has been disclosed, itshould be understood that a worker of ordinary skill in the art wouldrecognize many modifications come within the scope of this invention.For that reason, the following claims should be studied to determine thetrue scope and content of this invention.

1-18. (canceled)
 19. A system for measuring weight of an occupant seatedon a vehicle seat comprising: an inboard track assembly adapted formounting to a vehicle structure; an outboard track assembly spaced apartfrom said inboard track assembly and adapted for mounting to the vehiclestructure; a first sensor assembly mounted to a seat track of saidinboard track assembly for generating a first signal in response tomeasuring deflection of said inboard track assembly due to seat occupantweight; a second sensor assembly mounted to a seat track of saidoutboard track assembly for generating a second signal in response tomeasuring deflection of said outboard track assembly due to seatoccupant weight; and a central processor for determining seat occupantweight based on said first and second signals.
 20. The system accordingto claim 19 wherein said seat tracks of said inboard and outboard trackassemblies each have a predetermined cross-sectional area with each seattrack having at least one track portion with a cross-sectional area thatis less than said predetermined cross-sectional area, said first andsecond sensor assemblies being mounted on said track portions.
 21. Thesystem according to claim 20 wherein said seat tracks of said inboardand outboard track assemblies each have a forward end and a rearward endwith a central portion extending between said forward and rearward endsand wherein said forward and rearward ends are adapted for mounting tothe vehicle structure such that said central portions are unsupported toform a gap between the vehicle structure and said seat tracks.
 22. Thesystem according to claim 21 wherein said track portion with saidcross-sectional area that is less than said predeterminedcross-sectional area is located in said central portion.
 23. The systemaccording to claim 21 wherein said at least one track portion of each ofsaid inboard and outboard track assemblies is comprised of a first trackportion located forwardly in said central portion and a second trackportion located rearwardly in said central portion and wherein saidfirst and second sensor assemblies each include a first sensor mountedon said first track portion and a second sensor mounted on said secondtrack portion.
 24. The system according to claim 19 including an airbagcontrol module in communication with said central processor whereindeployment force of an airbag is controlled by said control module basedon seat occupant weight.
 25. The system according to claim 19 whereinsaid inboard and outboard track assemblies each have a first trackmember mountable to the vehicle structure and a second track membermounted for movement relative to said first track member via anadjustment assembly and wherein said first and second sensor assembliesare mounted to said first track members.
 26. The system according toclaim 19 wherein said first sensor assembly is directly mounted to saidseat track of said inboard track assembly and said second sensorassembly is directly mounted to said seat track of said outboard trackassembly.
 27. The system according to claim 19 wherein said seat tracksof said inboard and outboard track assemblies each have an unsupportedcentral track portion with said first and said second sensor assembliesbeing positioned at said central track portions of said seat tracks foreach of said inboard and outboard track assemblies.
 28. The systemaccording to claim 19 including an overload member cooperating with saidseat tracks of said inboard and outboard track assemblies to preventsaid inboard and outboard track assemblies from separating from thevehicle structure in response to overload forces.
 29. The systemaccording to claim 28 wherein said overload member comprises a fasteningelement that extends through at least one seat track portion.
 30. Amethod for determining weight of a seat occupant comprising the stepsof: providing an inboard seat track assembly adapted for mounting to avehicle structure and an outboard seat track assembly spaced apart fromthe inboard seat track assembly and adapted for mounting to the vehiclestructure; mounting a first sensor assembly to a track portion of theinboard seat track assembly; mounting a second sensor assembly to atrack portion of the outboard seat track assembly; generating a firstsignal from the first sensor assembly in response to deflection of theinboard track assembly due to seat occupant weight; generating a secondsignal from the second sensor assembly in response to deflection of theoutboard seat track assembly due to seat occupant weight; and combiningthe first and second signals to determine seat occupant weight.
 31. Themethod according to claim 30 including the step of providing a systemcontroller for controlling deployment of an airbag; generating a seatoccupant weight signal based on the combination of the first and secondsignals; transmitting the seat occupant weight signal to the controller;and controlling a deployment force of the airbag based on the seatoccupant weight.
 32. The method according to claim 30 including thesteps of providing the inboard and outboard seat track assemblies withforward ends and rearward ends interconnected by a center portion andfixing the forward and rearward ends to the vehicle structure such thatthe center portion of each seat track assembly remains unsupported. 33.The method according to claim 32 including the step of locating thefirst and second sensor assemblies in the center portion.
 34. The methodaccording to claim 30 wherein the first sensor assembly is comprised ofa first sensor mounted rearwardly within the inboard seat track assemblyand a second sensor mounted forwardly within the inboard seat trackassembly and wherein the second sensor assembly is comprised of a thirdsensor mounted rearwardly within the outboard seat track assembly and afourth sensor mounted forwardly within the outboard seat track assembly.35. The method according to claim 30 wherein the inboard and outboardseat track assemblies each have a first track member mountable to thevehicle structure and a second track member mounted for sliding movementrelative to the first track member and including the steps of mountingthe first sensor assembly to the first track member of the inboard seattrack assembly and mounting the second sensor assembly to the firsttrack member of the outboard seat track assembly.
 36. The methodaccording to claim 35 including mounting the first and second sensorassemblies directly to the first track members of the inboard andoutboard seat track assemblies.
 37. The method according to claim 30wherein the inboard and outboard seat track assemblies each include seattracks that are defined by a predetermined cross-sectional area andincluding forming at least one track portion with a cross-sectional areathat is less than the predetermined cross-sectional area, and mountingthe first and second sensor assemblies in the track portions having thecross-sectional area that is less than the predetermined cross-sectionalarea.
 38. The method according to claim 30 including the step ofpreventing the inboard and outboard seat track assemblies fromseparating from the vehicle structure in response to an overload force.